IAU 2006 General Assembly: Result of the IAU Resolution votes24. August 2006, Prague

The
first half of the Closing Ceremony of the 2006 International
Astronomical Union (IAU) General Assembly has just concluded. The
results of the Resolution votes are outlined here.

It is official: The 26th General Assembly for the International
Astronomical Union was an astounding success! More than 2500
astronomers participated in six Symposia, 17 Joint Discussions, seven
Special Sessions and four Special Sessions. New science results were
vigorously discussed, new international collaborations were initiated,
plans for future facilities put forward and much more.

In addition to all the exciting astronomy discussed at the General
Assembly, six IAU Resolutions were also passed at the Closing Ceremony
of the General Assembly:

Resolution 1 for GA-XXVI : "Precession Theory and Definition of the Ecliptic"

Resolution 2 for GA-XXVI: "Supplement to the IAU 2000 Resolutions on reference systems"

Resolution 3 for GA-XXVI: "Re-definition of Barycentric Dynamical Time, TDB"

Resolution 4 for GA-XXVI: "Endorsement of the Washington Charter for Communicating Astronomy with the Public"

Resolution 5A: "Definition of 'planet' "

Resolution 6A: "Definition of Pluto-class objects"

The IAU members gathered at the 2006 General Assembly agreed that a
"planet" is defined as a celestial body that (a) is in orbit around the
Sun, (b) has sufficient mass for its self-gravity to overcome rigid
body forces so that it assumes a hydrostatic equilibrium (nearly round)
shape, and (c) has cleared the neighbourhood around its orbit.

This means that the Solar System consists of eight "planets"
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. A new
distinct class of objects called "dwarf planets" was also decided. It
was agreed that "planets" and "dwarf planets" are two distinct classes
of objects. The first members of the "dwarf planet" category are Ceres,
Pluto and 2003 UB313 (temporary name). More "dwarf planets" are
expected to be announced by the IAU in the coming months and years.
Currently a dozen candidate "dwarf planets" are listed on IAU's "dwarf
planet" watchlist, which keeps changing as new objects are found and
the physics of the existing candidates becomes better known.

The "dwarf planet" Pluto is recognised as an important proto-type of
a new class of trans-Neptunian objects. The IAU will set up a process
to name these objects.

Below are the planet definition Resolutions that were passed.

Notes for editors
A press conference about the Closing Ceremony of the General Assembly,
including the results of the planet-definition vote, will be held at
18:00, in Meeting Room 3.3 of the Prague Congress Center. (It will NOT
be possible for journalists to ring in to this conference: they must be
there in person.)

The IAU is the international astronomical organisation that brings
together distinguished astronomers from all nations of the world. Its
mission is to promote and safeguard the science of astronomy in all its
aspects through international cooperation. Founded in 1919, the IAU is
the world's largest professional body for astronomers. The IAU General
Assembly is held every three years and is one of the largest and most
diverse meetings on the astronomical community's calendar.

Contacts
Following the vote, some of the members of the planet definition
committee will be available for interviews (after the final vote):

Programme for the Closing Ceremony: http://www.astronomy2006.com/second-session-and-closing-ceremony.php

Live public webcast of the Closing Ceremony: http://astronomy2006.com/tv/

Live press webcast of the Closing Ceremony (press only, please do not distribute): http://www.astronomy2006.com/tv-press

The IAU Web page: http://www.iau.org

IAU News during the 2006 General Assembly: http://www.iau2006.org

IAU General Assembly: http://www.astronomy2006.com

Free registration for the media: http://www.astronomy2006.com/media-accreditation.php

RESOLUTIONS
Resolution 5A is the principal definition for the IAU usage of "planet" and related terms.

Resolution 6A creates for IAU usage a new class of objects, for
which Pluto is the prototype. The IAU will set up a process to name
these objects.

IAU Resolution: Definition of a Planet in the Solar System
Contemporary observations are changing our understanding of planetary
systems, and it is important that our nomenclature for objects reflect
our current understanding. This applies, in particular, to the
designation 'planets'. The word 'planet' originally described
'wanderers' that were known only as moving lights in the sky. Recent
discoveries lead us to create a new definition, which we can make using
currently available scientific information.

RESOLUTION 5A
The IAU therefore resolves that "planets" and other bodies in our Solar
System be defined into three distinct categories in the following way:

(1) A "planet"1 is a celestial body that (a) is in
orbit around the Sun, (b) has sufficient mass for its self-gravity to
overcome rigid body forces so that it assumes a hydrostatic equilibrium
(nearly round) shape, and (c) has cleared the neighbourhood around its
orbit.

(2) A "dwarf planet" is a celestial body that (a) is in orbit around
the Sun, (b) has sufficient mass for its self-gravity to overcome rigid
body forces so that it assumes a hydrostatic equilibrium (nearly round)
shape2 , (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

(3) All other objects3 except satellites orbiting the Sun shall be referred to collectively as "Small Solar-System Bodies".

1The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.2An IAU process will be established to assign borderline objects into either dwarf planet and other categories.3These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.

IAU Resolution: Pluto

RESOLUTION 6A
The IAU further resolves:

Pluto is a "dwarf planet" by the above definition and is recognized as
the prototype of a new category of trans-Neptunian objects.1

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